Keira Knightley Can't Keep Her Clothes On

Once again the skinny actress has been photographed naked while doing a photo shoot for an ad campaign.

There have been bets when she will go full nude. Keira finds the bet hilarious," adds a source.

The Atonement star first stripped for a Vanity Fair cover alongside actress Scarlett Johansson in 2006, and has since participated in racy shoots for Coco Chanel and Interview magazine.